Electronic musical instrument



Sept. 26, 1939. a SWLEY 2,178,888

ELECTRONIC MUSICAL INSTRUMENT Filed March 28, 1938 MASTER oscmmon V72 ca AMPunER J mm. 22

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improved electronic umrso STATES PATENT OFFICE 2.11am uacraosrc nmsrosr. ms'raomr Gilbert Smiley, Hingham. Ill a-ignor to Hammond Instrument Company, Chicago, Ill,

a corporation of Delaware Application March 28, 1938, Serial No. 198,818

iclaims.

My invention relates generally to electronic musical instruments, and more particularly to improved key controlled circuits therefor.

It is an object of my invention to provide an musical instrument in which there is provided an oscillator generator for each note of the musical scale which oscillates continuously and supplies a signal to an electrode of a control tube, the grid bias of which is normally m such as to render-the control tube non-conducting, but in which means are provided to change the bias to permit transmission of the oscillator generator signal to an output circuit wherein the signal may be amplified and translated into 15 sound.

A further object is to provide an electronic musical instrument in which the transmission of the .tone signal to the output circuit is controlled by a repeater or control tube having key con- 20 trolled means for changing the grid bias in a manner to produce a note having rapid attack and slow decay.

A further object is to provide an improved key circuit for electronic musical instruments.

25 A further object is to provide an improved key circuit for electronic musical instruments in which the signal from a generator is distorted to introduce higher harmonics, and thus increase the harmonic development of the tone.

A further object is to provide an electronic musical instrument in which a key' controlled repester or distorter control tube is provided to cause changes in the harmonic development of the note produced as well as changes in the ina tensity thereof.

Other objects will-appear from the following description, reference being had to the accompanying drawing which shows a wiring diagram of a representative portion of the complete instrumentembodying my invention.

The instrument comprises generally a keyboard whichmaybesimilartothat ofthepianoor organ, a series of generators, one for each frequency of the musical scale, a control or repeater tube, the grid bias of which is controlled by means of a key circuit so as selectively to render the control tube capable oi conducting the signal which is continuously supplied thereto by its associated generator to an output circuit which 0 mavcompriseanampliiierandaloudspeaker.

As generators of the various frequencies required. I prefer, to use vacuum tube oscillators which maybe of the type disclosed and claimed in my Patent No. 2,083,348 granted Jime 8, 1937.

'l'heoscillatorsofaharmonieallyrelatedseries are preferably interconnected for frequency stabilization and, the highest frequency oscillator of the series preferably has its frequency stabilized by a master oscillator generating a frequency twice that of the controlled oscillator. The master oscillator may be of any suitable construction, but is preferably one of refined design which will very accurately maintain its frequmcy under varying conditions, and which, may be tuned with exac'titude. The master oscillator may also be provided with means for periodically shifting its rrequency slightly above and below its normal frequency of oscillation, thereby to introduce a vibrato effect which will be reflected by corresponding frequency changes in the series.

of oscillators controlled by the master oscillator. The master oscillator may also be utilized to pro vide a tone signal in a manner; similar to the method by which the remaining oscillators provide signals, or the master oscillator may function solely as a means for stabilizing the frequencies of oscillation of the series of oscillators stabilized thereby.

Inasmuch as the master oscillator may be of any suitable well-known design or construction, I have illustrated it diagrammatically as a block it, which is connected through a condenser Ci. resistor RI and resistor R2 with the grid G13 01 a tube T13, forming part of the oscillator for the generation of the signal for the note 13. (Assuming the notes of a standard piano to be numbered from i to 88, the highest A will be note No. 85, the A of the next lower octave will be note No. 73, etc.) The master oscillator it is provided for note No. 85 and in addition to furnishing a stabilizing signal to the grid of tube T13, may supply a signal to a key controlled output circuit (hereinafter to be described), although for tLe sake of simplicity, the key controlled circuit for the master oscillator has not been shown in the drawing. The grid bias for the tube T13 is supplied from a battery 30 through a potentiand a plate P13, the terminal it being connected to the gridGll through a mutual inductance l6 and a condenser CI providing a feed-back circuit. A portion of the winding of the mutual. inductance I6 is connected to ground through an adiustable contact n. The cathode an may be or" I azrasaa sity envelope of the note sounded will resemble that of a piano note or the note of a picked or plucked string, in that it will have very rapid attack, and gradual logarithmic decay. Upon release of the key, it will be returned to normal tion of the tube and terminating the sounding of the note. The completion of the circuit upon the engagement of the switch arm 28 with the contact Ill, will thus act in a manner similar to the dampers of a piano which engage the strings immediately upon release of the keys, and cause the strings to ceasevibrating.

By proper selection of the values of the condenser CS, resistor R5 and potential sources Bd and Eve, the rate of decay of the note may be predetermined to simulate that of the piano note or the notes of other similar instruments employingpicked or plucked strings as the sound producing means.

The tube V13 not only serves to control the intensity envelope of the note, but also acts as a distorter tube to change the shape of the wave produced by the oscillator including the tube TT'I. This function of the tube V13 and its associated circuit is fully pointed out in my prior Patent No. 2,038,892 dated April 7, 1936, and my aforesaid Patent No. 2,083,246. Assuming the signal produced by the oscillator and impressed upon the grid GVI3 is a sine wave, the value of the potential source Bd may be so chosen that when its potential is impressed upon the grid GVIJ, only the positive peaks of the signal wave will be effective to render the tube V" conducting. As more fully described in my aforesaid patent, this will result in the introduction by the tube V13 of a series of higher harmonics which will greatly enhance the quality of the tone produced by the instrument. As flle potential of the grid GVII drifts negatively toward cutoff potential (as the condenser C5 discharges), the shape of the wave form of the signal transmitted by the tube GVIJ will also change, thereby producing a change in the degree of harmonic development as'the tone decays.

In an instrument of the piano type. there will, of course, be 88 oscillators (76 if the master oscillators are used to supply the twelve highest frequencies) similar to that comprising the tube T13, and in the drawing two additional oscillators comprising tubes '1'" and tubes Tl! are shown, these oscillators generating frequencies for the notes II and I! of 880 and 440 cycles respectively. The elements of these oscillators may be identical with those of the oscillator previously described, except that there may be changes in the values of the elements of the circuits. It will therefore be unnecessary to describe them in detail. Similar reference characters have, however, been applied to the corresponding parts.

The frequency of the oscillator comprising the tube Til is stabilized by the signal produced by the oscillator TII. This stabilizing signal. is transmitted from the terminal ll through a conductor 42 which is connected to the grid circuit of the tube '1'" in the same manner that the master oscillator I0 is connected to the grid circuit of the tube T13. prising the tube Til impresses a frequency stabilizing signal upon the grid circuit of the tube master oscillator.

- in the art that numerous 'claims to include within Similarly, the oscillator com- 3 T through a conductor 44, and the oscillator comprising the tube T48 supplies a stabilizing signal to the grid circuit of the tube for the oscillator for note No. 37 (not shown) through a conductor 6. In this way, a plurality of oscillators may be tied together so that their frequencies will be stabilized and controlled by the The oscillators which are illustrated bear octave relationship to each other. As pointed out in my aforesaid Patent No. 2,083,- 246 the relationship between the oscillators may be of any other harmonic relationship. The plates Pvil and PV are connected through blocking condensers C4 and resistors R1, to a terminal 48 by a conductor ill. Thus the outputs of all the repeater control tubes are connected in parallel to supply their signals to the amplifier II. 1

From this it will be apparent that by tuning the master oscillator the series of oscillators controlled thereby will be correspondingly tuned, and similarly, ifqthe frequency of oscillation of the master oscillator is periodically shifted through a small range at a vibrato periodicity, the frequencies of the series of oscillators, controlled thereby will be shifted proportionately, and the notes produced will thus give a very desirable vibrato effect.

While I have disclosed but a single embodiment of my invention it will be apparent to those skilled changes may be made without departure from the basic principles thereof. I therefore desire by the following the scope of my invention all such constructions whereby substantially the same results may be obtained by substantially the same or equivalent means.

I claim:

1. In an electrical musical instrument, the combination of a plurality of generators of electrical impulses of the frequencies of the musical scale, an output circuit including an amplifying and electro-acoustic. translating means, and means for selectively controlling the transmission of impulses from said generators to said output circuit, said means comprising a multi-electrode thermionic tube for each of said generators, said tube having a control grid normally receiving impulses from its associated generator, means for biasing said control grid beyond extinction potential, a selectively operable key, a condenser associated with said grid biasing means, means operated by said key during the downward stroke thereof to increase the charge on said condenser to cause the grid bias on said tube to decrease upon depression of said key, and a resistor connected to said condenser gradually to decrease the charge thereof during the interval that said key is held depressed.

2. In an electrical musical instrument, the combination of a plurality of generators of elec-- trical impulses of the frequencies of the musical scale, an output circuit including an amplifying andelectro-acoustic translating means, and means for selectively controlling the transmission of impulses from said generators to said output circuit, said means comprising a multi-electrode thermionic tube for each of said generators, said tube having a control grid normally receiving impulses from its associated generator, means for biasing said control grid beyond extinction potential, a selectively operable key, a switch closed only during the down stroke of said key, and .a circuit associated with said switch to decrease the grid bias on said tube.

3. In an electrical musical instrument, the combination 0! a plurality of generators of electrical impulses of fundamental frequencies of the notes of the musical scale, a multi-electrode thermionic control tube for each of said generators and having a control electrode continuously receiving impulses from its associated generator, means for normally biasing said tube beyond cutoil to render said tube non-conducting, and selectively operable means to change the effective bias on said tube, said means comprising; a depressible key, means operated during initial portion only of the downward stroke of said key to render said biasingmeans ineffective and to render said tube conducting, and a condenser and resistance network for rendering said biasing means gradually more effective during the remainder of the down-stroke of said key and during theup-stroke of the key.

4. In an electrical musical instrument, the combination of a plurality of sources of electrical impulses of the frequencies ofthe musical scale,

a plurality of multi-electrode thermionic repeater control tubes each having a control grid, circuits for impressing impulses from said sources upon the grids of said tubes respectively, a negative potential source connected normally to bias the grid negatively beyond extinction potential, and means associated with each of said tubes to change the eflective grid potential thereof, said means comprising a selectively operable depressible key, a positive potential source, a resistor and condenser connected in parallel between said negative potential source and said grid, a switch temporarily closed by said key during only the initial portion of the down-stroke of the key, a circuit in parallel with said resistor and condenser and including said switch and said positive potential source, a' second switch closed only when said key is in normal inoperative position, and a negligible impedance circuit including said second switch and shunting said condenser and resistor when said second switch is closed. 20

GILBERT SMILEY. 

